1. Field of the Invention
The invention relates to methods for manufacturing field emission electron source and, particularly, to a method for manufacturing field emission electron source having carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios) (greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features tend to make CNTs ideal candidates for field emission electron sources.
Generally, a field emission electron source having CNTs includes a conductive base and CNTs formed on the conductive base. The CNTs acts as emitter of the field emission electron source. The methods adopted for forming the CNTs on the conductive base mainly include mechanical methods and in-situ synthesis methods. The mechanical method is performed by respectively placing single CNT on a conductive base by an Atomic force microscope (AFM), then fixing CNT on the conductive base by conductive pastes or adhesives. However, the controllability of the mechanical method is less than desired, because single CNT is so tiny in size.
The in-situ synthesis method is performed by coating metal catalysts on a conductive base and synthesizing CNTs on the conductive base directly by means of chemical vapor deposition (CVD). However, the mechanical connection between the CNTs and the conductive base often is relatively weak and thus unreliable. In factual use, such CNTs are easy to be drawn away from the conductive base due to the electric field force, which would damage the field emission electron source and/or decrease its performance. Furthermore, the shield effect between the adjacent CNTs may reduce the field emission efficiency thereof.
What is needed, therefore, is a controllable method for manufacturing a field emission source employing CNTs, which has a firm mechanical connection between CNTs and the conductive base, and has a high field emission efficiency.